Sky & Telescope - November 2023 - 53

1917 DRAWING: V. M. ZLATINSKY / IZVESTIA OBSHCHESTVA MIROVEDENIYA
(1917); JUPITER WITH DARK BARGE: DAMIAN PEACH
half a dozen descriptions of extremely
dark spots suggestive of impact scars.
However, Hockey concluded that many
of these features were merely " barges "
- dark reddish-brown cyclonic vortices
in Jupiter's atmosphere that often
have sharply defined elliptical outlines
and usually appear within or along the
northern edge of the planet's North
Equatorial Belt.
Cosmic collisions were the furthest
Vladimir Zlatinsky's sketch depicting his
extraordinary " black spot " on August 18, 1917
World War I shortly after the outbreak
of revolution in Russia.
Eight nights later Zlatinsky observed
thing from my mind back in 1999 when
I was perusing a copy of The Nature of the
Planets by Russian astronomer Vsevolod
Sharonov, originally published as Priroda
Planet in 1958. The 1964 English edition
features an extensive bibliography loaded
with references unfamiliar to most
Western readers. One of these titles
immediately caught my eye: Zlatinsky, V.
M., " Chernoe pyatno na Yupitere " [ " Black
Spot on Jupiter " ], Izvestia Obshchestva
Mirovedeniya. Vladimir Zlatinsky of the
University of Kazan's Engelhart Observatory
described a very strange dark
marking on Jupiter that he observed in
August 1917.
The planet wouldn't reach opposition
until late November that year, so in
mid-August it was a prominent object in
the predawn sky. On August 18th, Zlatinsky
trained a 4.3-inch refractor on
Jupiter. Using a magnification of 185×,
he was struck by a " sharp, elliptical and
very dark spot in the North Tropical
Zone . . . The round trailing edge of the
back of the spot I at first assumed to be
the shadow of one of Jupiter's moons,
but I was perplexed by the unusual
appearance of this 'shadow.' "
On the following day Zlatinsky
consulted an ephemeris and realized
that no shadow transit had occurred
the previous night. Later that day he
received the latest issue of the German
journal Astronomische Nachrichten
(Astronomical News), containing
a report by Philipp Fauth, Germany's
leading Jupiter observer, announcing
his discovery in early July of an exceptionally
dark, " violin-shaped " spot
in the North Tropical Zone spanning
more than 13° of longitude. I'm utterly
amazed that the publication managed to
reach Zlatinsky during the third year of
the feature for the second time and
found the spot " . . . so prominent at
the present time that it is the darkest
feature on the planet and should be
called the 'black spot' to differentiate
it from the Great Red Spot, with which
it has much in common: both are
located in the tropical zone on either
side of the equator and are of about the
same width. "
I'm struck by the fact that when
This September
28, 2011 image
of Jupiter records
an unusually
dark barge and
the shadow of
Jupiter's moon
Io - features that
can be mistaken
for impact scars.
Zlatinsky first glimpsed his " black
spot " he mistook part of it for a satellite
shadow. His sketch clearly records
two barges along the northern edge of
the nearby North Equatorial Belt, but
he depicts the darkness of these features
as far more muted than the black
spot. If the length of the black spot on
August 26th was comparable to that
of the Great Red Spot, which spanned
a whopping 33° of longitude in 1917,
it would have more than doubled in
length since Fauth measured it in early
July. This evolution calls to mind the
shearing of the Shoemaker-Levy 9 and
Wesley impact scars into long, irregular
streaks by prevailing east-west
winds. Was the 1917 feature really an
impact scar that was all but overlooked
during one of modern history's most
tumultuous years? While the descriptions
are very suggestive, there's no
mention of undiminished contrast
near the planet's limb that would constitute
" smoking-gun " evidence of it
being an impact scar.
If Sánchez-Lavega's 7-year-frequency
estimate is correct, we're long overdue
for the appearance of a visible impact
scar. That thought makes me want to
observe Jupiter every chance I get! The
planet reaches opposition on the 3rd
this month.
¢Contributing Editor TOM DOBBINS is
hoping that the smoke from Canadian
wildfires clears before Jupiter's opposition
this month.
sk yand tele scope .o r g * NOVEMBER 2023 53
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Sky & Telescope - November 2023

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